The present invention relates to foldable convertible top. More particularly this invention concerns a method of making such a top.
U.S. Pat. No. 5,267,770 of Orth describes a folding convertible top having a cover with a pair of full-length front-to-back seams that join a center panel to a pair of side panels. This cover is made of a flexible waterproof textile and is stretched over a rack having a plurality of transverse ribs. As the rack is folded up to lower the top, the cover is therefore folded transversely of the seams which buckle and are crushed together as the cover is fitted into the rear storage compartment. As a result the cover is severely stressed along these seams so that cracks eventually develop, leading to leaks and an unattractive appearance.
The cover described in German utility model 82 05 999 is basically made of two panels joined along a transversely extending seam. It can fold along a line on or parallel to this seam to reduce stress. Such a top is however somewhat complex to manufacture since it has several parts, and can leak at the seam.
In U.S. Pat. No. 6,183,037 of Bauer the convertible top is molded of a single smooth piece. Such a top is very attractive, but is made by an extremely complex process so that it is very costly.
It is therefore an object of the present invention to provide an improved foldable convertible top.
Another object is the provision of such an improved foldable convertible top which overcomes the above-given disadvantages, that is which is of inexpensive construction yet which is quite attractive.
A further object is to provide an improved method of making a foldable convertible top.
A cover for a foldable convertible top has according to the invention an outer foil having an inner face, and a foam-plastic core layer bonded over the entire bonding-foil inner face and itself having an inner face. The outer foil can be a one-piece slush-molded foil or it can be a highly stretchable and a thin thermoplastic bonding foil can be provided between the outer foil and the core layer. The core layer can be formed as described in commonly owned U.S. Pat. No. 6,340,196.
When not slush molded, the outer foil has 300% to 400% stretchability so that it can conform perfectly to the complex three-dimensional shape that the convertible top must have. It is a polyacrylate about 20 xcexcm thick. The bonding layer is of thermoplastic polyurethane.
According to the invention an inner polyurethane foil is bonded over the entire core-layer inner face. This provides it with a nonabsorbent inner surface that is easy to maintain clean and can easily be tinted to the desired decor color.
When the outer foil is slush-molded it normally 1 mm to 2 mm thick. The slush-molded outer layer has a roughened inner surface and is a two-component polyurethane.
Normally according to the invention the core layer has a Shore D hardness of about 40 and is formed with at least one inwardly open groove so that the cover can fold readily along the groove. The core layer is 7 mm to 8 mm thick but is only about 2 mm thick at the groove.
The core layer can further be unitarily formed in accordance with the invention with at least one inwardly projecting rib and the outer foil is stretched and tightly bonded over the rib. The rib is formed wholly by the core layer and outer foil or, if desired, a reinforcement strip is imbedded in the rib.
The convertible-top cover according to the invention is made according to the invention by first laying in a mold cavity of a first mold part a highly stretchable outer foil and then sucking the foil into tight engagement with an inner surface of the cavity. Then a second mold part is fitted over the first mold part to close the cavity and an expandable polyurethane foam is introduced into the cavity so that the foam fills the cavity and presses the foils together against the first mold part. The foam is cured in the cavity. Then the cured workpiece is demolded and trimmed to size.
It is also possible to fit an inner foil to the second mold part so that the foam is introduced between the inner and bonding foils. This provides an easy-to-clean lining for the convertible top.
In addition a thin thermoplastic bonding layer can be applied over the outer foil in the first mold part before the resin is injected in and the mold is closed. Alternately the outer foil is slush-molded, either right in the second mold part or in a separate mold. It has the exact complex three-dimensional finished shape of the outer surface of the convertible top.
The convertible-top cover according to the invention has no seams at all. Instead it is a single unitary construction that can be certain not to leak and to have a nice aerodynamic appearance. It can be made inexpensively since there is no complex stitching and fitting operation, being ready to use after demolding and trimming. The polyurethane core layer is a very good sound and heat insulator and can be molded to any desired shape since it has no seams.
When the outer layer is slush molded of Elastolan(copyright) (Elastogran GmbH) or of a thermoplastic polyurethane from the Recticel firm. The outer foil can be a polyurethane foil (e.g. Walopur(copyright) or Platilon(copyright) of Epurex Films GmbH) about 20 xcexcm to 70 xcexcm thick. Such an outer layer is completely water impervious so that it will ensure that the convertible top is water tight.